1 Introduction

[[https://travis-ci.org/guicho271828/lisp-namespace][https://travis-ci.org/guicho271828/lisp-namespace.svg?branch=master]]
#+BEGIN_SRC
Long time ago, in a galaxy far far away...
It is a period of a civil war. Lisp-2
aliens, striking from the function
namespace, have fought for the
design of their language against lisp-1.
#+END_SRC
tl;dr; → skip to API definition https://github.com/guicho271828/lisp-namespace#macro-define-namespace
+ update (2016/5/14) : added support for `documentation` and `describe`.
+ update (2016/5/21) : works on ECL, CLISP, ABCL and CMUCL.
* Introduction
# However, destructuring is merely
# a syntax sugar for writing the accessor.
There are several libraries which extends =let=. To my knowledge,
most of them goes toward destructuring, e.g., allowing
=&some-fancy-directive= in the argument list. However, destructuring is
now **obsolete**: superseded by pattern-matching (e.g. fare-matcher, optima, trivia), which
cleanly combines =cond=, =typecase=, destructuring and constructors[1].
Now it comes to my mind: what could be the *orthogonal* aspect
that could be combined with =let=, or, =let + cond = pattern matching= ?
Then I noticed an oddness in flet, macrolet, labels, let,
symbol-macrolet. Pattern matching works in the value namespace only.
# Also,
# while special bindings for /namespaces/ can be trivially implemented with a
# hash table, the lexical binding is not
--- it's worth a library. This is
what this library is for.
[1] Like =(cons A B)= matching clause vs =(cons A B)= constructor.
* Namespaces in CL?
By /namespace/ I don't mean a /package/,
which is a way to manage symbols. It is orthogonal to /namespace/.
CL already has major 2 namespaces, /function/ namespace and /value/
namespace (or /variable/ namespace), but there are actually more --- e.g.,
/class/ namespace. Since the same symbol can represent different
objects in each namespace, this is obviously orthogonal to /package/.
For example, all these below can coexist in a
same file without errors, and each object is accessible with the
corresponding function.
#+BEGIN_SRC lisp
(in-package :cl-user)
(defclass foo () ())
(defun foo () nil)
(defvar foo 1)
(find-class 'foo) ; -> #
(symbol-function 'foo) ; -> #
(symbol-value 'foo) ; -> 1
(make-instance 'bar) ; -> SIMPLE-ERROR
(symbol-function 'bar) ; -> UNDEFINED-FUNCTION
(symbol-value 'bar) ; -> UNBOUND-VARIABLE
#+END_SRC
| namespace | accessor | unbound condition | boundp | binding |
|-----------+-----------------+--------------------+---------+-------------|
| class | find-class | SIMPLE-ERROR | n/a | n/a |
| function | symbol-function | UNDEFINED-FUNCTION | fboundp | flet,labels |
| value | symbol-value | UNBOUND-VARIABLE | boundp | let |
/Some/ namespaces in CL can be said to overlap with each other. For example:
+ *class* namespace --- with *type*, *condition* and *struct* namespace
+ *function* namspace --- with *macro-function* and *generic-function* namespace
+ *value* namespace --- with *symbol-macro* namespace.
** Macro DEFINE-NAMESPACE
: (define-namespace name &optional (expected-type t) (binding t) (documentation ""))
This macro defines a namespace. For the given name of namespace X,
DEFINE-NAMESPACE defines 4 functions/macros:
+ =#'symbol-x, #'(setf symbol-x)= : accessor to the global binding. Optionally,
=expected-type= provides =ftype= proclamation and results in the
better optimization. =expected-type= is not evaluated.
+ =#'x-boundp= : unary function returning a boolean
+ condition =UNBOUND-X= which is signaled when trying to access the value of an unbounded symbol.
+ macro =(X-LET (binding...) body)= : lexical binding. Can be turned off
when =binding= is nil.
** Extending the usability of =documentation= and =describe=
=define-namespace= also defines a method for =cl:documentation= and extend =cl:describe-object=. For example, you will be able to =(setf (documentation 'mysymbol 'x) "description")= and you will see it pretty printed in =(describe 'mysymbol)=.
Here is an example used in TRIVIA pattern matcher. Trivia has an =assoc= pattern, and everyone would feel happy if we can browse the documentation of this pattern from SLIME C-c C-d. Below is such an output on SBCL.
While such a practice is taken by some libraries (e.g. QL-HTTP and Stefil defines =describe= methods), those facility is made independently, and this feature is not much popular.
#+begin_src diff
COMMON-LISP:ASSOC
[symbol]
ASSOC names a compiled function:
Lambda-list: (ITEM ALIST &KEY KEY (TEST NIL TESTP)
(TEST-NOT NIL NOTP))
Declared type: (FUNCTION
(T LIST &KEY (:KEY (OR FUNCTION SYMBOL))
(:TEST (OR FUNCTION SYMBOL))
(:TEST-NOT (OR FUNCTION SYMBOL)))
(VALUES LIST &OPTIONAL))
Documentation:
Return the cons in ALIST whose car is equal (by a given test or EQL) to
the ITEM.
Known attributes: call, foldable, flushable, unsafely-flushable
Source file: SYS:SRC;CODE;LIST.LISP
+Symbol ASSOC is bound in a namespace PATTERN:
+ Value: #
+ Documentation:
+ It matches when the object X is a list, and then further matches the contents
+ returned by (cdr (assoc item X...)) against SUBPATTERN.
+ If :KEY and :TEST is specified, they are passed to ASSOC.
#+end_src
Note that /namespace/ itself has its own namespace. The optional argument =documentation= to =define-namespace= is a docstring of the namespace itself. It will be set to =(setf (documentation NAME 'namespace) documentation)= and will also be visible from =describe=.
Examples are in [[EXAMPLE.org]] .
* Expected Usecase?
Every time you want to define a =define-cool-object= macro. E.g.,
+ in [[https://github.com/guicho271828/eazy-project][eazy-project]], [[https://github.com/guicho271828/eazy-project/blob/master/src/defmenu.lisp#L24][defmenu]]
+ in [[https://github.com/AccelerationNet/function-cache][function-cache]], [[https://github.com/AccelerationNet/function-cache/blob/master/src/cache.lisp#L4][defcached]] (currently implemented with hash tables)
+ in [[https://github.com/m2ym/optima][optima]], [[https://github.com/m2ym/optima/blob/master/src/pattern.lisp#L337][defpattern and pattern-expand-function]] (currently implemented
with symbol properties)
+ in [[https://github.com/Bike/compiler-macro][compiler-macro]], [[https://github.com/Bike/compiler-macro/blob/master/hint.lisp#L10][define-compiler-hinter]] (currently implemented with hash tables)
+ in [[https://github.com/cffi/cffi][cffi]], [[https://github.com/cffi/cffi/blob/master/src/libraries.lisp#L129][define-foreign-library]] (currently implemented with hash tables)
* Other misc
** Macro NAMESPACE-LET / NSLET
=LET= with ability to lexically bind any value in the namespace.
It currently supports /function, labels, value, symbol-macro, macrolet,
restart, handler/ [2] namespaces and the user-defined namespaces.
Full examples are in [[EXAMPLE.org]] .
#+BEGIN_SRC lisp
(namespace-let ((#'x (y) (1+ y))
((macro x) (y) (1+ y))
((macro y) (y) (1+ y))
(#'x (y) (1+ y))
((label y) (y) (y y))
((symbol-macro sm) 0)
(b 0))
(let ((b 1))
(print :x)))
;; (PROGN
;; (FLET ((X (Y) (1+ Y)))
;; (MACROLET ((X (Y) (1+ Y))
;; (Y (Y) (1+ Y))) ; same kinds of bindings are merged
;; (FLET ((X (Y) (1+ Y)))
;; (LABELS ((Y (Y) (Y Y)))
;; (SYMBOL-MACROLET ((SM 0))
;; (LET ((B 0))
;; (PROGN
;; (LET ((B 1))
;; (PRINT :X))))))))))
#+END_SRC
[2] restarts and handlers have the dynamic scope only.
** Package LISP-NAMESPACE
it has =(:nicknames lispn)= .
* Design?
I'm wondering which abbreviation to =namespace-let= is appropriate.
It should be something consistent with the historic name as =let=.
However, I do not like names like =let+= because they are not
self-expressive --- =let+= does not describe how it's different from the
original =let=. =bind= and =where= are not considered good either, due to the
similar reason.
I adopted =nslet=, thanks to masatoi0@twitter's
advice. However, there is another alternative: Make it =let= and force the
user to shadow =cl:let=? (nah I don't like it.) I'm still searching for a
crazy bright idea.
Here are the remaining TODOs:
+ X-let does not recognize =(declare (special ...))= currently.
* Dependencies
This library is at least tested on implementation listed below:
+ SBCL 1.2.8 on X86 Linux 3.13.0-44-generic (author's environment)
+ CCL 1.10-r16196 (LinuxX8664)
Also, it depends on the following libraries:
+ alexandria by ** :
Alexandria is a collection of portable public domain utilities.
* Author & Copyright
Copyright (c) 2015 Masataro Asai (guicho2.71828@gmail.com)
Licensed under the LLGPL License.